Two kinds of charge: attract and repel
There are two kinds of charge, called positive and negative. Like charges repel and unlike charges attract. When two surfaces are rubbed, one loses electrons and becomes positive, the other gains them and becomes negative, and the two charges are equal and opposite. For example, glass rubbed with silk becomes positive while the silk becomes negative. Ebonite rubbed with wool becomes negative while the wool becomes positive. Which material gains electrons depends on the pair, so there is no single rule for all materials. A charged object also attracts a light uncharged object, such as paper: in the paper the charges shift a little, so the side nearest the comb has the opposite charge and is pulled. In electrostatic painting, the paint drops are charged and the object is given the opposite charge, so the paint is attracted evenly and less is wasted.
| Rubbed pair | Gets electrons | Loses electrons |
|---|---|---|
| glass with silk | silk (−) | glass (+) |
| ebonite with wool | ebonite (−) | wool (+) |
Predict, then try with an adult on a dry day. Rub two balloons on wool in the same way and hang them side by side from threads. Do they push or pull? Then hold a rubbed plastic comb near them. Before each step write down your prediction using the words like, unlike, attract and repel. Never use mains electricity and never test in a storm.